Protective grating for a mass flow rate sensor in a channel of suctioned air

ABSTRACT

The present invention relates to a device for measuring at least one parameter of a medium flowing in a line, particularly the intake-air volume of an internal combustion engine. Liquid particles contained in the line act upon a measuring element and influence a characteristic curve of the measuring element which is used to determine parameters of the flowing medium. The characteristic curve of the measuring element can be changed disadvantageously by solid-matter particles. According to the present invention, to reduce the action of solid-matter particles on the measuring element ( 23 ), a protective grating ( 15 ) is proposed in which side walls ( 36 ) of channels ( 43 ) of the protective grating ( 15 ) form various angles of intersection with the flow direction ( 6, 12 ). Solid-matter particles are thereby diverted into a path of motion ( 53 ) around the measuring element ( 23 ).

BACKGROUND INFORMATION

[0001] The present invention is based on a device for measuring at least one parameter of a medium flowing in a line according to the species defined in claim 1.

[0002] The German Patent 197 35 891 A1 describes a measuring body, insertable into a clean channel of an intake line of an internal combustion engine, for determining the mass of the intake air, which has a flow channel and a measuring channel that is essentially inclined in relation to a longitudinal axis of a line, and which subdivides into an S-shaped deflection channel adjoined thereto. A measuring element is arranged in the measuring channel. The measuring element can be constructed as a micromechanical sensor part having a dielectric membrane, as is known, for example, from the German Patent 43 38 891 A1 and the U.S. Pat. No. 5,452,610, respectively. Because of the entry of water into the intake line, for example, due to a roadway wet from rain, the measuring element may become contaminated. Natural components of dissolved salts contained in this spray water then cause a drift in the characteristic as the result of the buildup of salt crusts on the membrane of the sensor part. It may be that the inclination of the measuring body forms a screened region, however, dirt or liquid particles nevertheless get into the measuring channel.

[0003] From the German Patent 197 35 664 A1, a device is already known in which the measuring element is positioned within a tubular member through which the medium flows, an upstream end of the tubular member extending into a filter chamber, and there having inlet openings on a lateral surface to reduce the action of dirt particles or water droplets on the measuring element. Particularly in the case of heavily polluted air and a high water content in the intake air of the internal combustion engine, the danger exists that the air filter will become saturated with water which then passes through the filter mat and, in so doing, takes along dirt particles. On the downstream side of the air filter, the actual clean side, the danger now exists that the intake air will again carry along dirt particles and water droplets from the filter surface which then deposit in an undesirable manner on the measuring element, and which lead to measuring errors or a malfunction of the measuring element. By the arrangement of the inlet openings on the lateral surface, the tubular member according to the related art reduces the danger of deposits on the measuring element; however, a correspondingly long design of the tubular member causes an undesirable pressure drop which leads to a decrease in measuring sensitivity. In addition, given a fluid entry of 20 liter/hour resulting during operation of a motor vehicle, the reduction of the action of liquid/solid-matter particles on the measuring element is too small. The German Patent 196 52 753 A1 describes a device having a measuring element, the device containing a flow rectifier and a grating for stabilizing a measuring signal. However, no further grating or element is used to protect the measuring element from liquids or solid-matter particles.

[0004] It has furthermore been proposed to use a repelling grating in a line to separate liquid particles from streaming air or a gas. Such a repelling grating, connected upstream of an inner pipe or in the line, influences the air/water mixture streaming toward the measuring element in such a way that the liquid particles are guided to a pipe wall or a line wall, while the air remains in a center of the inner pipe.

[0005] A different characteristic appears in response to the throughput of a mixture with air and dust in the line. Because of its still higher inertia compared to a liquid, the dust, in response to a change in the direction of flow forced by the side walls employed, changes its path only by reflection at the side wall, the principle of angle of incidence equal to angle of reflection being valid. Depending on the orientation of the side wall and the point of impact, a certain particle rejection thereby results, that is to say, a certain portion of the particles striking on the repelling grating is deflected by a reflection in the direction of the wall. The remaining part, after two reflections at the side walls, once more exhibits the main flow direction, and thus can strike, unhindered, on the measuring element downstream of the repelling grating.

SUMMARY OF THE INVENTION

[0006] In comparison, the device of the present invention having the characterizing features of claim 1 has the advantage that the deflection of solid-matter particles and liquid particles is improved in a simple manner by varying the orientation of the side walls with respect to the main flow direction over their extension in the main flow direction.

[0007] Advantageous further developments and improvements of the device indicated in claim 1 are rendered possible by the measures specified in the dependent claims.

[0008] It is advantageous to influence the path of motion of the solid-matter particles in the streaming medium by the formation of the side walls in such a way that it runs past the measuring element, since in this manner, the measuring element is not soiled.

[0009] The possibility of positive or negative angles of intersection of the side walls with the flow direction has the advantage that it permits more variations in the design.

[0010] The continuous curve of a channel has the advantage that the danger of a separation of the flow possibly arising is reduced, whereby otherwise an increased signal noise is caused.

[0011] A particularly advantageous formation of the channel is given in dependent claim 7.

[0012] The use of a tubular member in the line of the device has the advantage that additional protection is attained for the measuring element.

BRIEF DESCRIPTION OF THE DRAWING

[0013] Exemplary embodiments of the present invention are represented in a simplified manner in the Drawing, and are explained more precisely in the description below. FIG. 1 shows an example of a device according to the present invention in a pipe stub; FIG. 2 shows an axial cross-section in the longitudinal direction in FIG. 1; FIG. 3 shows a uniflow-current channel according to the related art; FIGS. 4a and b show an axial cross-section through a uniflow-current channel constructed according to the present invention; FIGS. 5a and b show further exemplary embodiments of the device according to the present invention in partial representation.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0014]FIG. 1 shows a device 1 for measuring at least one parameter, particularly an air-volume flow, of a medium flowing in line 2, especially the intake-air volume of an internal combustion engine.

[0015] Parameters of a flowing medium are, for example, the air-volume flow for ascertaining an air mass, a temperature, a pressure or a flow velocity, which are determined by suitable sensors. It is possible to use device 1 for measuring further parameters. This can be carried out by using two or more sensors, one sensor also being able to ascertain two or more parameters. Line 2 has a wall 3. The medium flows in line 2 in main flow direction 6, indicated by an arrow. Line 2 has an inner wall 7. Provided in line 2 is, for example, a tubular member 8 running with radial clearance with respect to line 2 and circumflowed by the medium. Tubular member 8 has a flow-through channel 11 and a protective grating 15 situated in the region of its upstream end. Plastic, metal, ceramics or glass can be used as material for protective grating 15. For example, plate-shaped protective grating 15 made of plastic can be produced by injection molding or by introducing grating openings 44 using a material-removing method. Downstream, somewhat removed from protective grating 15, a flow direction 12 prevails in flow-through channel 11. Flow direction 12 runs, let us say, parallel to main flow direction 6. Line 2 has a center line 27 which, for example, is also the center line of tubular member 8.

[0016] For instance, a measuring member 19 extends into tubular member 8. For example, measuring member 19 is partially inserted through an insertion opening 31 in wall 3 and an insertion opening 22 in a wall of tubular member 8, and projects with a free end into flow-through channel 11. One skilled in the art is familiar with such a measuring member 19 from the German Patent 197 35 891 A1, which is intended to be part of this disclosure. The air volume drawn in by the internal combustion engine is arbitrarily alterable by a throttle valve (not shown), positioned downstream of tubular member 8 in the intake manifold of the internal combustion engine.

[0017] To ascertain the intake-air mass of the internal combustion engine, measuring member 19 is provided which has an essentially elongated and rectangular-shaped design and which extends along a longitudinal axis 21. Longitudinal axis 21 runs essentially perpendicular to center line 27, and consequently also to main flow direction 6. In this context, a connector end of measuring member 19 accommodating the electrical connections, e.g. in the form of blade contacts, remains, for instance, outside of line 2. Provided in known manner in measuring member 19 is a measuring element 23 that is in contact with the air flowing through flow-through channel 11 and by which the air-volume flow drawn in by the internal combustion engine is determined. For example, measuring element 23 can be a temperature sensor as is known from the German Patent 42 28 484 C2, a pressure sensor as is used in the German Patent 31 35 794 A1, or an air-volume sensor, which ascertains the corresponding parameters. Selected here as an example for the various sensors is an air-volume sensor which, for instance, is arranged in measuring member 19 that, for example, has an inlet opening 20 into which the medium flows. For example, measuring element 23 can be constructed in known manner in the form of at least one temperature-dependent resistor. In particular, it is possible, as is described, for example, in the German Patent 43 38 891 A1 and the U.S. Pat. No. 5,452,610, respectively, to construct measuring element 23 as a micromechanical component which has a dielectric membrane upon which resistor elements are formed. It is also conceivable to introduce measuring element 23 into line 2 or tubular member 8 without measuring member 19. Located on tubular member 8 are, for instance, at least two braces 33 which are used to support tubular member 8 in line 2.

[0018] In addition to supporting tubular member 8 in the air flow between line 2 and tubular member 8, braces 33 cause an increase in the pressure drop, so that the air quantity flowing through flow-through channel 11 increases, and secondly, braces 33, in an intended manner, bring about a rectification of the intake-air flow. Tubular member 8 can also be arranged in line 2 without braces 33, e.g., it is secured to measuring member 19.

[0019] A design of protective grating 15 is clarified more precisely in the following FIGS. 2, 4 and 5. To that end, only briefly:

[0020] Liquid droplets deposit on protective grating 15 and are conducted to an inner wall 7 of line 2 or of tubular member 8, and thereby move past inlet opening 20 of measuring member 19 or past measuring element 23.

[0021] Further downstream of protective grating 15, a flow direction 12, which is nearly parallel to the center line of tubular member 8, prevails in flow-through channel 11.

[0022]FIG. 2 shows an axial cross-section in the longitudinal direction in FIG. 1. The same reference numerals as in FIG. 1 are used for identical or equally-acting parts. Protective grating 15 can be seen having side walls 36 which run inclined by a specific deflection angle with respect to center line 27. Side walls 36 are, for example, parallel to plug-in axis 21 and perpendicular to plug-in axis 21, or stand perpendicular one upon the other and are arranged in any orientation about center line 27. Side walls 36 form channel openings 44 which, at least transverse to flow direction 6, 12, are triangular, or are round or oval, or are four-cornered as in this exemplary embodiment. The medium flows in through channel openings 44 and, viewed downstream, leaves protective grating 15 diverted in a different direction 45, indicated by an arrow, after protective grating 15. For example, it is also possible to provide no tubular member 8, so that, for instance, protective grating 15 extends over the entire cross-section of line 2. Measuring member 19 has a front surface 48 against and around which the medium flows first. A lower surface 55 is formed by the free radial end of measuring member 19.

[0023] A channel 43, formed by two side walls 36, has, for example, a first section 49 in which side wall 36 forms an angle of intersection α with flow direction 12. In a second section 50, side wall 36 of channel 43 forms an angle of intersection β with flow direction 12 which is larger than angle of intersection α.

[0024]FIG. 3 shows a channel 43 of a protective grating 15 according to the related art. The medium flows into channel opening 44 of channel 43 in main flow direction 6. Distributed uniformly over the cross-section of channel opening 44 are twenty lines 53 which show paths of motion of one particle each in channel 43. A part of the particles is reflected once at only one side wall 36 and thereupon leaves channel 43 again downstream in a direction 45. Direction 45 runs at an angle δ to flow direction 12. Angle δ is different from zero. A certain portion of lines 53 shows paths of motion in channel 43 with double reflection, one reflection each at each of side wall 36, so that these particles leave a channel outlet again downstream approximately parallel to flow direction 12, and thus are able to strike unhindered on measuring element 23 provided downstream.

[0025]FIGS. 4a and b show two examples of the design according to the present invention of protective grating 15 of device 1. FIG. 4a shows a channel 43 of protective grating 15 which has, for example, a first section 49 and a second section 50 downstream. The side-wall sections bounding first section 49 form with flow direction 12 an angle of intersection α which here, for example, is 25° C. The side-wall sections bounding second section 50 form with flow direction 12 an angle of intersection β which, for example, is 35° C. The number of paths of motion of individual representing lines 53 which, upon emergence from channel 43, run parallel to flow direction 6, 12 downstream of channel 43 has been reduced compared to the related art according to FIG. 3. Improvement of the protection of measuring element 23 from striking particles is thereby ensured.

[0026]FIG. 4b shows an exemplary embodiment of channel 43 having an angle of intersection β which, in this case, is 45°. The angles of intersection can be positive and negative, i.e. all or only a part of them can be negative.

[0027]FIGS. 5a and b show further exemplary embodiments of channel 43. FIG. 5a shows a channel 43 whose upper side wall 56 forms an equal angle of intersection with flow direction 12 in all sections. Lower side wall 57 opposite upper side wall 56 has, for example, two sections. First section 49 forms an angle of intersection α with flow direction 12, and the second section forms an angle of intersection β with flow direction 12 deviating from angle of intersection α. The difference with respect to the channel formation according to FIG. 4a is that lines 53, which are reflected in the region of upper side wall 56 in second section 50, are reflected with an equal angle of intersection α.

[0028]FIG. 5b shows a channel 43 whose side wall 36 is continuously curved, so that a different angle of intersection α, β, γ is formed with flow direction 12 at each location of the side wall, the danger of a separation of the flow possibly arising thereby being reduced. 

What is claimed is:
 1. A device (1) for determining at least one parameter, particularly a volumetric flow, of a medium in the form of a gas/liquid/solid-matter particle mixture, especially the intake air of an internal combustion engine, flowing in a line (2), having a measuring element (23) arranged in the line (2) and circumflowed by the flowing medium, wherein the device (1) has at least one protective grating (15) arranged at least partially upstream of the measuring element (23) within the line (2), the protective grating having at least one channel (43) which at least partially diverts the medium, flowing in a main flow direction (6), downstream after the protective grating (15), and has at least one side wall (36) having at least two sections (49, 50) which form at least one angle of intersection (α, β) differing from one another, with the flow direction (6, 12).
 2. The device as recited in claim 1, wherein, viewed in the flow direction (6, 12), the path of motion (53) of the solid-matter particles of the flowing medium, due to at least a single reflection at the side wall (36), after the emergence from the channel (43), runs in such a way after the protective grating (15) that it forms an angle (γ) with the flow direction (6, 12), and the solid-matter particles are led past the measuring element (23) situated further downstream.
 3. The device as recited in claim 1, wherein the angles of intersection (α, β) are positive or negative.
 4. The device as recited in one or both of claims 1 or 2, wherein the at least one channel (43) of the protective grating (15) is continuously curved in the flow direction (6, 12).
 5. The device as recited in one or more of the preceding claims 1, 2 or 4, wherein the at least one channel (43) has a channel opening (44) through which the medium gets into the channel (43), and a cross-section of the channel opening (44) transverse to the flow direction (6, 12) is at least triangular.
 6. The device as recited in one or more of the preceding claims 1, 2, 4 or 5, wherein a cross-section of the channel opening (44) transverse to the flow direction (6, 12) is round or oval.
 7. The device as recited in claim 1, wherein the channel (43) has two sections (49, 50); the first section (49) forms an angle of intersection of approximately 25°, and the second section (50) forms an angle of intersection of approximately 35° with the main flow direction (6, 12).
 8. The device as recited in one or more of the preceding claims, wherein a tubular member (8), through which the medium flows in the main flow direction (6), extends in the line (2) and has a flow-through channel (11), and the measuring element (23) is situated in the tubular member (8). 